1. Field of the Invention
The present invention relates to a method of maintaining the development activity of a photographic lithographic developer employed in an automatic developing machine constant and, more particularly, it is concerned with an improvement in a method of maintaining the development activity constant by using two kinds of replenishers differing in free sulfite ion concentrations, bromide ion concentrations and pH.
2. Description of the Prior Art
When photographic processings are carried out on an industrial scale, it becomes necessary to control various development process conditions, for instance, temperature, time, agitation, developer, development activity, etc., used.
In order to control development activity, a supplemental amount of a developer has been added to a developer solution being used for every photosensitive material processed so as to maintain the development activity constant. This method is, in general, called "replenishment" in the photographic art. Therefore, the present invention relates to a method of replenishing a photographic lithographic developer.
The activity of the developer decreases principally due to the following factors:
(a) Development reactions taking place at the time of the development-processing of films (which will be described hereinafter as "processing exhaustion" for brevity) affect the developer activity. Namely, development of films causes various chemical effects to occur in the developer used. Examples of such effects include a decrease in the concentration of the developer, an increase in the concentration of the oxidation products of the developing agent accompanying the above-described decrease in developer concentration, and the liberation of halide ions from the silver halide present in the developed films into the developer used.
(b) Natural deterioration occurs in the developer stored in a tray or a tank, and aerial oxidation of the developer occurs spontaneously by reaction with oxygen in the air (which will be described hereinafter as "time-passage exhaustion" for brevity).
When development-processing using an automatic developing machine is allowed to continue for a long time of several days to several months, both factors (a) and (b) above take place causing a decrease in the development activity of the developer used.
Since each of these two factors influences the developer in individual and different ways, an assumption regarding the relative extents of the influence exerted by the two factors described above on the developer must be made so that the composition of replenisher to be added can be determined.
Where a number of films are development-processed successively on a regular basis during the twenty-four hours of every day using an automatic developing machine which is operated continuously, a supplemental amount of the developer is added for every processing depending on the quantity consumed by the previous processing. That is to say, since the rate of consumption of the developer can be regarded as approximately constant on such an occasion, satisfactory results can be achieved by addition of replenisher to compensate for processing exhaustion for the processing of each film in the amount necessary to replenish for the consumption of the developer occurring in the processing of each film.
However, in operation, an automatic developing machine is not used continuously, for example, the processing of films is stopped at night or over the weekend. Therefore, the factor (b) described above also influences the developer used. Such being the case, if only a replenisher to compensate for process exhaustion is added, the development activity of the developer cannot be maintained constant.
In photographic development-processing which has been predominantly carried out in the past, the quantity of the replenisher to compensate for process exhaustion to be added has been determined on the basis of the amount of developed silver halide present in the developed film, which depends upon, for example, the size of the film developed, the blackened area of the film developed, the kind of film developed and the characteristic of the developed image (e.g., whether the image is positive or negative).
The photographic speed of the developer to be used should be evaluated before processing by measuring the blackened density which is obtained by developing a control film strip having a latent image therein due to a prior exposure to light with an exact exposure, with the developer. The quantity of replenisher to be added can be adjusted on the basis of the change in the density of the developed image formed on the control film strip. When the blackened density of the control film strip obtained is lower than the initial value, replenisher should be added to the developer.
In addition, replenishment to compensate for the decrease in the development activity occurring in the developer resulting from the passage of time has been conventionally carried out by adding a replenisher having a composition similar to or different from that of the replenisher used to compensate for process exhaustion in an amount determined by the blackened density of a control film strip in a similar manner to the case of deterioration caused by the development-processing. Using this approach, however, only the photographic speed of the developer can be restored to the initial level.
In the replenishing method to compensate for deterioration due to the passage of time as described above, the amount to be supplemented has been determined by trial and error. Therefore, the determination of the optimum amount to be supplemented requires a lot of work and a long period of time and, further, there is a great concern that photographic characteristics such as the quality of the dots and the half-tone gradation related to the tone reproduction of the original image cannot be restored completely to the level obtained using a fresh developer, even though the sensitivity can be restored to the initial level by the addition of replenishers. More specifically, it is impossible to restore the development activity accurately to the level obtained using a fresh developer in accordance with the replenishing method described above.
Moreover, an automatic replenishing system for the developer is disclosed in Japanese Patent Application (OPI) No. 5436/1971 (corresponding to British Patent No. 1,313,796), wherein the content of halides present in the developer and the concentration of the developer are monitored and the information obtained thereby is analyzed, followed by the appropriate use of two kinds of replenishers in which the concentrations of halide ions in each corresponds to the requirements obtained from the analysis. In this replenishment system, two kinds of solutions having different halide ion concentrations are employed. One contains a low concentration of halide ions. The other contains a high concentration of halide ions; that is to say, almost the same concentration as that desired in the developer. The replenisher with a lower concentration of halide ion may be added in a conventional manner, namely, depending on the amount of films passed through the developer. The other replenisher having a higher concentration of halide ion may be added when restoration of the development activity lost by aerial oxidation is essential, but the concentration of halide ion must be maintained as it is without change, which occurs sometime after the use of the developer. However, such an automatic replenishing system possesses serious disadvantages that the apparatus employed as the monitor is, in general, very expensive and the maintenance of the apparatus requires much time and labor.
Methods for replenishment by adding replenishers to compensate for process exhaustion and to compensate for time-passage exhaustion where the components of the replenishers are different are disclosed in German Patent Application (OLS) No. 2,004,893 and in U.S. Pat. No. 4,025,344.
However, in each of these methods, the disclosure is of the addition of replenishers where the components of the replenisher to compensate for exhaustion due to processing and the components of the replenisher to compensate for exhaustion due to ageing, which occurs during operation of the automatic developer machine, are different. No considerations are taken in these methods for the time-passage exhaustion which also occurs when the automatic developing machine is turned off and operation is suspended.
Where the suspension time is short, i.e., the automatic developing machine is turned off for a short period of time, the time-passage exhaustion which occurs during the suspension of the automatic developing machine can be neglected. However, where the suspension time continues for a long period of time, the time-passage exhaustion during the suspension must be considered. Especially, when the developer used is a lithographic developer, processing in a stable manner would not be achieved, if one neglects the time-passage exhaustion which occurs during the time of suspension, when the automatic developing machine is turned off and not operated.
Since the change in the composition of the developer due to ageing mainly comprises a decrease in free sulfite ion concentration, therefore, this change in developer composition does not cause a change to occur in visual sensitivity. However, with lithographic development, the dot quality is affected greatly by the decrease in free sulfite ion concentration and if exhaustion due to ageing which occurs during suspension of operation is neglected, it is impossible to maintain the true development activity of the developer constant.
The true development activity can be only maintained constant when compensation for the time-passage exhaustion of the developer, particularly a lithographic developer, which occurs during a suspension of the automatic developing machine is made.